Spring snowpack anomaly patterns and winter climatic variability

The objective of this study was to describe the spatial and temporal structure of spring snowpack anomalies in British Columbia, Canada, and to relate the anomaly patterns to climatic fluctuations. Cluster analysis was used to identify relatively homogeneous groups of snow course sites, based on the April 1 snowpack measurements, for the periotd 1966–1992. Time series of cluster-averaged anomalies were then computed. Synoptic-scale circulation types were defined by applying a correlation-based map classification technique to gridded data sets of surface pressure and 500-hPa height levels. Frequencies of the circulation types were calculated for each winter (November to March). Total precipitation and mean temperature for each winter were calculated from monthly data from 16 climate stations. Snowpack anomalies from 1966 to 1976 were dominated by two patterns: one characterized by generally heavier-than-average snowpacks over most of the province and the other by heavier-than-average snowpacks in the south and lighter-than-average in the north. From 1977 to 1992, snowpack conditions were generally either lighter than average over the whole province or were heavier than average in the north and lighter than average in the south. Snowpack and precipitation were generally correlated, although at some stations it appears that high winter temperatures, likely causing more midwinter melt and more rain, can act to reduce the snowpack. The differences in anomaly patterns and frequencies of synoptic types between the 1966–1976 and 1977–1992 periods accord with decadal-scale shifts in sea surface temperatures and atmospheric circulation patterns over the North Pacific, as reported in the literature. The shift in snowpack anomaly patterns following 1976 is consistent with reported shifts in glacier mass balance and rates of retreat and with streamflow fluctuations.